Powered wipers for automotive-vehicle windows and especially the rear windows of station wagons and other vehicles in which the window has a steep incline or is substantially upright, have gained widespread acceptance in the art since a window wiper is capable of clearing the rear windows of dirt and other view-obstructing substances which tend to collect upon the rear window of the vehicle when the latter travels through wet streets because of the vortex action of the air stream trailing the vehicle. In its rest position, the window wiper lies against the window at the lower edge thereof so as not to obstruct the view of the driver.
For the heating of automotive vehicles and especially the rear window of an automotive vehicle, e.g. for deicing and defrosting thereof, resistance-heating wires are imbedded in the glass pane in a number of passes so that, upon the passage of electrical current through the heating wire, the temperature of the window is raised to a level sufficient to melt ice and prevent the formation of view-obstructing condensates thereon.
To prevent obstruction of the visibility of the driver of the vehicle, the window is generally provided with the resistance wires only over an upper portion of the window so that the lower portion thereof provides a free field of view. In addition this confinement of the wires to the upper part of the window prevents overloading of the current source energizing the resistance heating wires. In general, therefore, the lower portion of the window is free from resistance heating wires.
Upon icing up of the rear window, the wiper frequently freezes to the window along its lower edge and, upon actuation of the wiper motor, may cause the rubber blade to tear or cause other damage to the drive system. While the section of the window provided with the resistance heating wires is rapidly defrosted, the low conductivity of the window pane results in a delayed release of the wiper and hence the latter is only freed after substantial delay when the heat from the exhaust gas stream reaches the window.
Because of the generally widespread use of salt on the road, it is not uncommon that the roadways are wet even though the temperature is below freezing. Consequently the rear window may be coated with dirt even when the upper portion has been defrosted and the wiper is still incapable of clearing the lower portion which is intended to provide a free field of view.